1. Field
The presently disclosed subject matter relates to devices, systems, and processes useful as a control system for a gear reduction assembly, and in particular, for automatically selecting between a low range drive ratio and a high range drive ratio.
2. Description of the Related Art
Typical four-wheel drive vehicles have a transfer case that is a separate powertrain component from the engine and the multi-ratio transmission. The transfer case supplies the drive torque to each of the front and rear axles in series with the transmission. Shift-on-the-fly gear selection allows automatic selection between two-wheel drive and four-wheel drive while the vehicle is in motion. An electronic control unit (ECU) can select two or four-wheel drive based on several input variables, including road conditions, engine load, wheel slip, acceleration, driver input, and other variables.
The transfer case typically includes a gear reduction assembly that provides a high range drive ratio for normal driving speeds and a low range drive ratio for low driving speeds such as when the vehicle is driven off-road, when high torque is desired, when low traction surfaces exist, etc. For example, the low range drive ratio can be used when starting from a stop on an incline with a trailer in tow (i.e., when engine load is high). Each of the high range drive ratio and the low range drive ratio can be used with any one of the reverse drive ratio and the plurality of forward drive ratios available in the multi-ratio transmission.
In these known four-wheel drive configurations, selection of the low range drive ratio or the high range drive ratio is initiated by the driver. The driver can physically cause the shift by moving a shift lever mounted in the passenger compartment that is mechanically connected to the gearing in the transfer case. Movement of the lever by the vehicle driver engages the selected one of the low range drive ratio and the high range drive ratio.
Alternatively, the driver can initiate the shift between the low range drive ratio and the high range drive ratio by actuating an electrical switch in the driver area of the passenger compartment. The electrical switch signals an ECU that drives actuator(s) to shift between the low range drive ratio and the high range drive ratio.
In each of these driver-initiated configurations, the low range drive ratio will not be engaged until the driver takes a deliberate action. Thus, it is possible for the high range drive ratio to remain engaged when it might be otherwise prudent to engage the low range drive ratio. Similarly, the low range drive ratio may remain engaged long after it is necessary for given vehicle operation parameters. Thus, fuel economy, acceleration ability, and other vehicle performance can be compromised.
Accordingly, there is a need to provide a fully automated control of the selection of the low range drive ratio and the high range drive ratio without a specific prompt from the driver, as well as to provide operating parameters for an ECU that provide efficient and accurate automatic switching between the low range drive ratio and high range drive ratio.